Short answer, I would not use gly on marginals or shoreline plants. It tends to bond with soil molecules, then is supposed to dissipate from there. In water, it does not, and can cause contamination. Trout, as well as most fishes have a lot of fatty tissues, which are like chemical sponges. They will soak up and store contminants, mercury, selenium, maybe even gly. Might not kill them, might kill whatever eats them.
We have a posted limit of how much Striped Bass you should eat per month out fo the Sacramento Delta. It's ounces. The toxic brew dumped into the water is the culprit, including mercury.
As far as your water plants, if you could take a live sample, still green, and lay it flat on a white sheet of paper 8 1/2 X 11, it helps a lot for the photo identification.
